"Scientists find [people who grew up poor] are more prone to illness than those who were never poor. Becoming more affluent may lower the risk of disease by lessening the sense of helplessness and allowing greater access to healthful resources like exercise, more nutritious foods and greater social support; people are not absolutely condemned by their upbringing. But the effects of early-life stress also seem to linger, unfavorably molding our nervous systems and possibly even accelerating the rate at which we age."

In one case, people who experienced early-life adversity were found to bear scars of that stress right in their DNA. Our telomeres (the tips of chromosomes) get shorter as we age, but people who grew up poor were found to have even shorter tips over time, suggesting accelerated aging.

And beyond the simple impact of stress on our bodies over time, studies have found that social hierarchy also plays a role in long-term health for the rich, the poor and everyone in between.

British epidemiologist Michael Marmot coined the term "Status Syndrome" to describe how people's health is often impacted by their social status.

"Conventional explanations for noncommunicable disease—lack of access to medical care, unhealthy lifestyles—at best only partially explain the status syndrome," Marmot wrote in a 2006 white paper. "Rather, the lower individuals are in the social hierarchy, the less likely it is that their fundamental human needs for autonomy and to be integrated into society will be met. Failure to meet these needs leads to metabolic and endocrine changes that in turn lead to increased risk of disease."

In a study of British civil servants, he found that even people relatively high on the social ladder had a lower sense of control and, thus, poorer health than those ahead of them.

"In other words it wasn't only the difference between top and bottom,"he said. "But where you were in the hierarchy was intimately related to your chances of health and disease."